barcode dll for vb net Grayscale versus Black-and-White in Software

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Grayscale versus Black-and-White
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What most people refer to as a black-and-white photo is called a grayscale image by people with a digital graphics background. In the computer graphics world, a black-and-white image can contain only black and white, while a grayscale image contains black, white, and shades of gray. I use the terms interchangeably in this book but thought I d give you a heads-up so that you ll know what s what if you get in a discussion with someone who s from the graphics side of the tracks. Also note that your photo editor may offer a command that converts your image to the Grayscale color model, which produces an image with 256 colors again, black, white, and shades of gray. When I speak of the Grayscale color model, with a capital G, I m referring to this particular type of file.
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aren t always found in the same channel. It also has an averaging effect that tends to reduce the tonal range of the image. As an example, study just the garlic clove in the images in Figure 8.7. The top left image shows the result of the standard grayscale conversion; the other three images show the original contents of the red, green, and blue channels. Some of the best shadow detail from the blue channel didn t survive the journey to the composite.
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Composite gray Red channel
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Green channel
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Blue channel
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FIGURE 8.7 You can split a digital camera image into its individual color channels, which reflect the amount of red, green, and blue light in the picture.
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By making the grayscale conversion yourself, you control how much brightness data comes from each channel. This enables you to pull out particular details that you want to emphasize to custom blend your own grayscale recipe.
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CHAPTER 8: Manipulating Color
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To do a custom blend, you have to look beyond the standard color-to-grayscale conversion found in every photo editor. (In Photoshop Elements, this command is Image | Mode | Grayscale and it converts the picture to the 256-color Grayscale mode discussed in the earlier sidebar Grayscale versus Black-and-White. ) The following list offers just a few of the other, better ways of going gray. You can compare the results on Page 31 of the color insert. Note that which techniques you can use depends on your photo software. For all but the first one, you need a program that gives you access to individual color channels. (Photoshop Elements and most comparably priced programs don t provide this feature.) Also, I didn t attempt to give each of the conversions the same tonal qualities because I wanted you to see just how much variation you can achieve.
In Photoshop Elements, use the Gradient Map command in combination with
the Hue/Saturation filter, as explained in the How-To sidebar Create Custom Grayscale Conversions in Photoshop Elements.
Convert the image to the Lab color mode. This color mode, used primarily by
imaging professionals, also comprises three color channels: a Lightness channel that stores just the pixel brightness data, plus two other channels for storing color information. The Lightness channel by itself often produces an excellent grayscale image. However, because photo printers are geared to outputting RGB images, you should copy the contents of the Lightness channel to a new RGB image instead of saving the file in the Lab mode. The red, green, and blue channels in your new image will all contain the same brightness values. (Again, see the sidebar Exploring RBG Color if all this channel stuff is foreign to you.)
You also may find that the original red, green, or blue channel contains just the
grayscale tones that you re after. If so, just copy that channel to a new RGB image.
In Adobe Photoshop, the Channel Mixer command enables you to specify exactly
what percentage of each RGB channel you want your grayscale image to contain. Other advanced imaging programs also offer this feature, although it may go by a different name.
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How To
CREATE CUSTOM GRAYSCALE CONVERSIONS IN PHOTOSHOP ELEMENTS
To control your color-to-black-and-white conversions in Photoshop Elements, follow these steps. Work on a copy of your original image file, as always.
1. Set the foreground and background colors to black and white, respectively. You can do this quickly by just pressing the D key (D for default colors). 2. Open the Layers palette and click the Layer Adjustment icon, labeled in Figure 8.8. Choose Gradient Map from the menu that appears.
Layer Adjustment icon FIGURE 8.8 The first step in the custom conversion process is to apply a black-to-white gradient map.
3. When the Gradient Map dialog box appears, choose the Foreground to Background gradient icon in the top drop-down list, as shown in Figure 8.8, and click OK. The program then maps your original image colors to a black-to-white spectrum. In other words, the darkest pixels become black,
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